This application claims the priority of Korean Utility Model Application No. 2002-22419, filed Jul. 26, 2002 in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a projection lens apparatus for a projector and a method of assembling same.
2. Description of the Related Art
With the development of information technology, and in order to satisfy people""s demands to observe an image on a large-scale screen, an image projecting apparatus, for example, an image projection apparatus using a liquid crystal display, is in growing demand.
An image projecting apparatus generally includes a projector for generating, expanding and projecting an image on a screen. According to the way of projection, the image projecting apparatus is usually categorized into a rear projection type or a front projection type.
FIG. 1 shows a rear projection type image projecting apparatus, which includes a cabinet 1 on which a screen 2 is mounted, a projector 3 mounted in the cabinet 1, and a reflective mirror 4 for reflecting the image emitted from the projector 3 towards the rear side of the screen 2.
The projector 3 includes a light source 11 for generating light, an image generating unit 12 for generating an image with the light, and a projection lens group 13 having a plurality of projection lenses for expanding and projecting the generated image towards the reflective mirror 4. The projection lens group 13 includes a first projection lens group 14 positioned in the proximity of the image generating unit 12, a second projection lens group 15 for expanding and projecting the image, and a reflection group 16 for reflecting the image passed through the first projection lens group 14 towards the second projection lens group 15. The second projection lens group 15 and the reflection group 16 are altogether secured in a main lens barrel 17 of a predetermined shape (FIG. 2). The first projection lens group 14 is supported on a rear lens barrel 18 to be movable forward and backward with respect to the main lens barrel 17, thereby adjusting the focus of image projected against the screen 2. In assembling the projection lens group 13, the rear lens barrel 18 is rotated to be moved forward and backward within and without the main lens barrel 17 so that the focus can be precisely adjusted. Then the rear lens barrel 18 is fixed in the main lens barrel 17.
The rear lens barrel 18 may be fixed in the main lens barrel 17 with adhesives such as a bond, or alternatively, with screws which are passed through the main lens barrel 17 and fastened to one side of the rear lens barrel 18. During such a fixing, however, a gap between the rear lens barrel 18 and the main lens barrel 17 hinders precise alignment of the rear lens barrel 18 during forward and backward motion. Even after the fixing, focus sometimes deviates due to the presence of the gap. In the case of using screws, the rear lens barrel 18 is deviated to a side by the pressing of the screws, thus, such a tilt causes degradation in the performance of the projection lens.
Accordingly, it is an aspect of the present invention to provide a projection lens apparatus of a projector having an improved structure which is capable of maintaining a focus of the projection lens even after assembly.
The above aspect is accomplished by a projection lens apparatus of a projector consistent with the present invention, comprising a main lens barrel comprising a first projection lens group that expands and projects an image that is incident thereto, and a reflection group that reflects the incident image towards the first projection lens group, a rear lens barrel provided with a second reflection group that projects the incident image towards the reflection group, the rear lens barrel being connected to the main lens barrel to move forward and backward to adjust an optical axis of the image as projected, and a pressing mechanism that elastically presses or means for elastically pressing the rear lens barrel with respect to the main lens barrel in the direction of the optical axis, thereby maintaining the rear lens barrel at a predetermined position so that the second projection lens group is not deviated from the optical axis.
The pressing mechanism includes a coil spring disposed within the main lens barrel and wound around an outer circumference of the rear lens barrel, the coil spring being elastically supported in the direction of the optical axis.
The rear lens barrel includes a fastening portion formed on one end, having a thread line on an outer circumference thereof and screw-engaged with an inner circumference of the main lens barrel, and a flange portion formed on the other end with the outer diameter thereof extending. The pressing mechanism includes a coil spring for being engaged around the outer circumference of the rear lens barrel with one end being supported on the flange portion.
The main lens barrel includes a thread line formed in an inner circumference for screw-engagement with the fastening portion of the rear lens barrel, with an inner diameter being stepped to support the other end of the coil spring.
In addition, the pressing mechanism prevents the formation of a gap between the main lens barrel and the rear lens barrel. The rear lens barrel comprises a body portion between said fastening portion and said flange portion. The body portion has a larger diameter then said fastening portion. The flange portion has a greater diameter that the body portion, wherein said flange portion supports one end of said pressing mechanism wound around the body portion.
It is another aspect of the present invention to provide a method of assembling a projection lens apparatus of a projector by screwing a rear lens barrel fitted to a main lens barrel, the method comprising guiding a fastening portion of said rear lens barrel along a thread line of the main lens barrel by rotating the rear lens barrel with respect to the main lens barrel, adjusting the optical axis of a second projection lens group supported on the rear lens barrel, and elastically holding the rear lens barrel with respect to the main lens barrel by compressing a pressing mechanism.